Effects of Uranium Stress on Photosynthetic Characteristics and Mineral Nutrition Metabolism of Different Bryophytes

【Objective】The study was conducted to investigate the effects of uranium pollution on chlorophyll fluorescence physiological characteristics and mineral element accumulation of bryophytes, and screen out bryophytes used for monitoring and remediation of environmental uranium pollution.【Method】In this study, Hypnum cupressiforme L. ex Hedw. var. cupressiforme, Thuidium cymbifolium and Racomitrium japonicum were used as biological materials to analyze the differences in chlorophyll contents, chlorophyll fluorescence parameters, uranium accumulation and mineral nutrient metabolism under different uranium stress concentrations（0, 2.5, 5, 10 and 20 mg/L）.【Result】The chlorophyll contents of three bryophytes were negatively related to the concentrations of uranium stress. Hymenoptera showed a high sensitivity to uranium stress, and its chlorophyll content was the first to be significantly suppressed, with a greatest decrease in chlorophyll content. Uranium stress had an inhibitory effect on Fv/Fm, Y（ Ⅱ ）, qP and qN of T. cymbifolium, a “low-promotion, highsuppression” effect on Y（Ⅱ）, qP, qN of H. cupressiforme L. ex Hedw. var. cupressiforme and Y（Ⅱ）, qP of R. japonicum, and a positive effect on qN of R. japonicum. The uranium accumulation of T. cymbifolium was significantly higher than that of H. cupressiforme L. ex Hedw. var. cupressiforme and R. japonicum under low, medium and high concentrations of uranium stress, which was directly proportional to the length of villi in leaves of three bryophytes. The uptake of K and Ca by bryophytes could be promoted by a certain concentration of uranium stress, but inhibited when the stress concentration was too high.【Conclusion】The changes of chlorophyll content, chlorophyll fluorescence physiological characteristics and the contents of K and Ca can be used as physiological indexes for screening out bryophytes to monitor and restore uranium pollution; T. cymbifolium is more sensitive to uranium stress than H. cupressiforme L. ex Hedw. var. cupressiforme and R. japonicum., and its ability to accumulate uranium is stronger than H. cupressiforme L. ex Hedw. var. cupressiforme and R. japonicum. Therefore, T. cymbifolium can be used as a preferred bryophyte for monitoring and restoring environmental uranium pollution.